Pulmonary problems in a wide variety of clinical settings often have their genesis in aspiration. We propose to document the incidence, determine predisposing causes, and try and prevent aspiration in a large group of critically ill patients. Since we have shown that tracheostomy tubes strongly predispose one to aspirate, a great deal of the work will be carried out in patients with tracheostomies using an Evans Blue Dye test. Aspiration in patients without tracheostomies will be detected by placing a heavy barium-tantalum mixture intraorally and then taking high KV tracheal xrays. In addition, since massive aspiration also requires regurgitation, the incidence of regurgitation will be documented in critically ill patients using a dye marker placed intragastrically. Experimental studies evaluating current therapy of aspiration pneumonia and new methods of treatment are to be carried out in an isolated perfused canine lobe. Steroids, albumin, and alkaline lavage are amongst modalities to be tested. Further information as to the pathogenesis of acid pulmonary injury will be obtained by following mucocilliary clearance rates following aspiration in dogs. Tantalum bronchograms will be utilized in this part of the study.